Process for removing sulfur from vacuum gas oil

Abstract

A process for removing a sulfur compound from a vacuum gas oil feed includes contacting the vacuum gas oil feed comprising the sulfur compound with a vgo-immiscible ionic liquid to produce a vacuum gas oil and vgo-immiscible ionic liquid mixture, and separating the mixture to produce a vacuum gas oil effluent having a reduced sulfur content relative to the vacuum gas oil feed.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 61/291,283 filed Dec. 30, 2009.

FIELD OF THE INVENTION

This invention relates to processes for reducing the sulfur content of vacuum gas oils (VGO). More particularly, the invention relates to removing sulfur contaminants from VGO using an ionic liquid.

BACKGROUND OF THE INVENTION

VGO is a hydrocarbon fraction that may be converted into higher value hydrocarbon fractions such as diesel fuel, jet fuel, naphtha, gasoline, and other lower boiling fractions in refining processes such as hydrocracking and fluid catalytic cracking (FCC). However, VGO feed streams having higher amounts of sulfur are more difficult to convert. For example, the degree of conversion, product yields, catalyst deactivation, and/or ability to meet product quality specifications may be adversely affected by the sulfur content of the feed stream. It is known to reduce the sulfur content of VGO by catalytic hydrogenation reactions such as in a hydrotreating process unit.

Various processes using ionic liquids to remove sulfur and nitrogen compounds from hydrocarbon fractions are also known. U.S. Pat. No. 7,001,504 B2 discloses a process for the removal of organosulfur compounds from hydrocarbon materials which includes contacting an ionic liquid with a hydrocarbon material to extract sulfur containing compounds into the ionic liquid. U.S. Pat. No. 7,553,406 B2 discloses a process for removing polarizable impurities from hydrocarbons and mixtures of hydrocarbons using ionic liquids as an extraction medium. U.S. Pat. No. 7,553,406 B2 also discloses that different ionic liquids show different extractive properties for different polarizable compounds.

There remains a need in the art for improved processes that enable the removal of compounds comprising sulfur from vacuum gas oil (VGO).

SUMMARY OF THE INVENTION

In an embodiment, the invention is a process for removing a sulfur compound from a vacuum gas oil comprising contacting the vacuum gas oil with a VGO-immiscible ionic liquid to produce a vacuum gas oil and VGO-immiscible ionic liquid mixture, and separating the mixture to produce a vacuum gas oil effluent and a VGO-immiscible ionic liquid effluent comprising the sulfur compound.

In an embodiment, the VGO-immiscible ionic liquid comprising at least one of an imidazolium ionic liquid, a pyridinium ionic liquid, and a phosphonium ionic liquid. In another embodiment, VGO-immiscible ionic liquid comprises at least one of 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-4-methylpyridinium chloride, N-butyl-3-methylpyridinium methylsulfate, trihexyl(tetradecyl)phosphonium chloride, trihexyl(tetradecyl)phosphonium bromide, tributyl(methyl)phosphonium bromide, tributyl(methyl)phosphonium chloride, tributyl(hexyl)phosphonium bromide, tributyl(hexyl)phosphonium chloride, tributyl(octyl)phosphonium bromide, tributyl(octyl)phosphonium chloride, tributyl(decyl)phosphonium bromide, tributyl(decyl)phosphonium chloride, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, triisobutyl(methyl)phosphonium tosylate, tributyl(ethyl)phosphonium diethylphosphate, and tetrabutylphosphonium methanesulfonate.

In a further embodiment, the mixture comprises water in an amount less than 10% relative to the amount of VGO-immiscible ionic liquid in the mixture on a weight basis; the mixture may be water free.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified flow scheme illustrating various embodiments of the invention.

FIGS. 2A and 2B are simplified flow schemes illustrating different embodiments of an extraction zone of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In general, the invention may be used to remove a sulfur compound from a vacuum gas oil (VGO) hydrocarbon fraction through use of a VGO-immiscible ionic liquid.

The terms “vacuum gas oil”, “VGO”, “VGO phase” and similar terms relating to vacuum gas oil as used herein are to be interpreted broadly to receive not only their ordinary meanings as used by those skilled in the art of producing and converting such hydrocarbon fractions, but also in a broad manner to account for the application of our processes to hydrocarbon fractions exhibiting VGO-like characteristics. Thus, the terms encompass straight run VGO as may be produced in a crude fractionation section of an oil refinery, as well as, VGO product cuts, fractions, or streams that may be produced, for example, by coker, deasphalting, and visbreaking processing units, or which may be produced by blending various hydrocarbons.

In general, VGO comprises petroleum hydrocarbon components boiling in the range of from about 100° C. to about 720° C. In an embodiment the VGO boils from about 250° C. to about 650° C. and has a density in the range of from about 0.87 g/cm³ to about 0.95 g/cm³. In another embodiment, the VGO boils from about 95° C. to about 580° C.; and in a further embodiment, the VGO boils from about 300° C. to about 720° C. Generally, VGO may contain from about 100 ppm-wt to about 30,000 ppm-wt nitrogen; from about 1000 ppm-wt to about 50,000 ppm-wt sulfur; and from about 100 ppb-wt to about 2000 ppm-wt of metals. In an embodiment, the nitrogen content of the VGO ranges from about 200 ppm-wt to about 5000 ppm-wt. In another embodiment, the sulfur content of the VGO ranges from about 1000 ppm-wt to about 30,000 ppm-wt. The nitrogen content may be determined using ASTM method D4629-02, Trace Nitrogen in Liquid Petroleum Hydrocarbons by Syringe/Inlet Oxidative Combustion and Chemiluminescence Detection. The sulfur content may be determined using ASTM method D5453-00, Ultraviolet Fluorescence; and the metals content may be determined by UOP389-09, Trace Metals in Oils by Wet Ashing and ICP-OES. Unless otherwise noted, the analytical methods used herein such as ASTM D5453-00 and UOP389-09 are available from ASTM International, 100 Barr Harbor Drive, West Conshohocken, Pa., USA.

Processes according to the invention remove a sulfur compound from vacuum gas oil. That is, the invention removes at least one sulfur compound. It is understood that vacuum gas oil will usually comprise a plurality of sulfur compounds of different types in various amounts. Thus, the invention removes at least a portion of at least one type of sulfur compound from the VGO. The invention may remove the same or different amounts of each type of sulfur compound, and some types of sulfur compounds may not be removed. In an embodiment, the sulfur content of the vacuum gas oil is reduced by at least 3 wt %. In another embodiment, the sulfur content of the vacuum gas oil is reduced by at least 20 wt %; and the sulfur content of the vacuum gas oil may be reduced by at least 80 wt %.

One or more ionic liquids are used to extract one or more sulfur compounds from VGO. Generally, ionic liquids are non-aqueous, organic salts composed of ions where the positive ion is charge balanced with negative ion. These materials have low melting points, often below 100° C., undetectable vapor pressure and good chemical and thermal stability. The cationic charge of the salt is localized over hetero atoms, such as nitrogen, phosphorous, sulfur, arsenic, boron, antimony, and aluminum, and the anions may be any inorganic, organic, or organometallic species.

Ionic liquids suitable for use in the instant invention are VGO-immiscible ionic liquids. As used herein the term “VGO-immiscible ionic liquid” means the ionic liquid is capable of forming a separate phase from VGO under operating conditions of the process. Ionic liquids that are miscible with VGO at the process conditions will be completely soluble with the VGO; therefore, no phase separation will be feasible. Thus, VGO-immiscible ionic liquids may be insoluble with or partially soluble with VGO under operating conditions. An ionic liquid capable of forming a separate phase from the vacuum gas oil under the operating conditions is considered to be VGO-immiscible. Ionic liquids according to the invention may be insoluble, partially soluble, or completely soluble (miscible) with water.

In an embodiment, the VGO-immiscible ionic liquid comprises at least one of an imidazolium ionic liquid, a pyridinium ionic liquid, and a phosphonium ionic liquid. In another embodiment, the VGO-immiscible ionic liquid is selected from the group consisting of imidazolium ionic liquids, pyridinium ionic liquids, phosphonium ionic liquids and combinations thereof. Imidazolium and pyridinium ionic liquids have a cation comprising at least one nitrogen atom. Phosphonium ionic liquids have a cation comprising at least one phosphorous atom.

In an embodiment, the VGO-immiscible ionic liquid comprises at least one of 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-4-methylpyridinium chloride, N-butyl-3-methylpyridinium methylsulfate, trihexyl(tetradecyl)phosphonium chloride, trihexyl(tetradecyl)phosphonium bromide, tributyl(methyl)phosphonium bromide, tributyl(methyl)phosphonium chloride, tributyl(hexyl)phosphonium bromide, tributyl(hexyl)phosphonium chloride, tributyl(octyl)phosphonium bromide, tributyl(octyl)phosphonium chloride, tributyl(decyl)phosphonium bromide, tributyl(decyl)phosphonium chloride, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, triisobutyl(methyl)phosphonium tosylate, tributyl(ethyl)phosphonium diethylphosphate, and tetrabutylphosphonium methanesulfonate. The VGO-immiscible ionic liquid may comprise at least one of 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-4-methylpyridinium chloride, N-butyl-3-methylpyridinium methylsulfate, trihexyl(tetradecyl)phosphonium chloride, trihexyl(tetradecyl)phosphonium bromide, tributyl(hexyl)phosphonium chloride, tributyl(octyl)phosphonium chloride, tetrabutylphosphonium chloride, and tributyl(ethyl)phosphonium diethylphosphate.

In another embodiment, the VGO-immiscible ionic liquid is selected from the group consisting of 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-4-methylpyridinium chloride, N-butyl-3-methylpyridinium methylsulfate, trihexyl(tetradecyl)phosphonium chloride, trihexyl(tetradecyl)phosphonium bromide, tributyl(methyl)phosphonium bromide, tributyl(methyl)phosphonium chloride, tributyl(hexyl)phosphonium bromide, tributyl(hexyl)phosphonium chloride, tributyl(octyl)phosphonium bromide, tributyl(octyl)phosphonium chloride, tributyl(decyl)phosphonium bromide, tributyl(decyl)phosphonium chloride, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, triisobutyl(methyl)phosphonium tosylate, tributyl(ethyl)phosphonium diethylphosphate, tetrabutylphosphonium methanesulfonate, and combinations thereof. The VGO-immiscible ionic liquid may be selected from the group consisting of 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-4-methylpyridinium chloride, N-butyl-3-methylpyridinium methylsulfate, trihexyl(tetradecyl)phosphonium chloride, trihexyl(tetradecyl)phosphonium bromide, tributyl(hexyl)phosphonium chloride, tributyl(octyl)phosphonium chloride, tetrabutylphosphonium chloride, tributyl(ethyl)phosphonium diethylphosphate, and combinations thereof. In an embodiment, the VGO-immiscible ionic liquid comprises 1-butyl-3-methylimidazolium trifluoromethanesulfonate.

In an embodiment, the invention is a process for removing sulfur from vacuum gas oil (VGO) comprising a contacting step and a separating step. In the contacting step, vacuum gas oil comprising a sulfur compound and a VGO-immiscible ionic liquid are contacted or mixed. The contacting may facilitate transfer of the one or more sulfur compounds from the VGO to the ionic liquid. Although a VGO-immiscible ionic liquid that is partially soluble in VGO may facilitate transfer or extraction of the sulfur compound from the VGO to the ionic liquid, partial solubility is not required. Insoluble vacuum gas oil/ionic liquid mixtures may have sufficient interfacial surface area between the VGO and ionic liquid to be useful. In the separation step, the mixture of vacuum gas oil and ionic liquid settles or forms two phases, a VGO phase and an ionic liquid phase, which are separated to produce a VGO-immiscible ionic liquid effluent and a vacuum gas oil effluent.

The process may be conducted in various equipment which are well known in the art and are suitable for batch or continuous operation. For example, in a small scale form of the invention, VGO and a VGO-immiscible ionic liquid may be mixed in a beaker, flask, or other vessel, e.g., by stirring, shaking, use of a mixer, or a magnetic stirrer. The mixing or agitation is stopped and the mixture forms a VGO phase and an ionic liquid phase which can be separated, for example, by decanting, centrifugation or use of a pipette to produce a vacuum gas oil effluent having a lower sulfur content relative to the vacuum gas oil. The process also produces a VGO-immiscible ionic liquid effluent comprising the one or more sulfur compounds.

The contacting and separating steps may be repeated for example when the sulfur content of the vacuum gas oil effluent is to be reduced further to obtain a desired sulfur level in the ultimate VGO product stream from the process. Each set, group, or pair of contacting and separating steps may be referred to as a sulfur removal step. Thus, the invention encompasses single and multiple sulfur removal steps. A sulfur removal zone may be used to perform a sulfur removal step. As used herein, the term “zone” can refer to one or more equipment items and/or one or more sub-zones. Equipment items may include, for example, one or more vessels, heaters, separators, exchangers, conduits, pumps, compressors, and controllers. Additionally, an equipment item can further include one or more zones or sub-zones. The sulfur removal process or step may be conducted in a similar manner and with similar equipment as is used to conduct other liquid-liquid wash and extraction operations. Suitable equipment includes, for example, columns with: trays, packing, rotating discs or plates, and static mixers. Pulse columns and mixing/settling tanks may also be used.

FIG. 2A illustrates an embodiment of the invention which may be practiced in sulfur removal or extraction zone 100 that comprises a multi-stage, counter-current extraction column 105 wherein vacuum gas oil and VGO-immiscible ionic liquid are contacted and separated. The vacuum gas oil or VGO feed stream 2 enters extraction column 105 through VGO feed inlet 102 and lean ionic liquid stream 4 enters extraction column 105 through ionic liquid inlet 104. In the Figures, reference numerals of the streams and the lines or conduits in which they flow are the same. VGO feed inlet 102 is located below ionic liquid inlet 104. The VGO effluent passes through VGO effluent outlet 112 in an upper portion of extraction column 105 to VGO effluent conduit 6. The VGO-immiscible ionic liquid effluent including the sulfur compounds removed from the VGO feed passes through ionic liquid effluent outlet 114 in a lower portion of extraction column 105 to ionic liquid effluent conduit 8.

Consistent with common terms of art, the ionic liquid introduced to the sulfur removal step may be referred to as a “lean ionic liquid” generally meaning a VGO-immiscible ionic liquid that is not saturated with one or more extracted sulfur compounds. Lean ionic liquid may include one or both of fresh and regenerated ionic liquid and is suitable for accepting or extracting sulfur from the VGO feed. Likewise, the ionic liquid effluent may be referred to as “rich ionic liquid”, which generally means a VGO-immiscible ionic liquid effluent produced by a sulfur removal step or process or otherwise including a greater amount of extracted sulfur compounds than the amount of extracted sulfur compounds included in the lean ionic liquid. A rich ionic liquid may require regeneration or dilution, e.g. with fresh ionic liquid, before recycling the rich ionic liquid to the same or another sulfur removal step of the process.

FIG. 2B illustrates another embodiment of sulfur removal washing zone 100 that comprises a contacting zone 200 and a separation zone 300. In this embodiment, lean ionic liquid stream 4 and VGO feed stream 2 are introduced into the contacting zone 200 and mixed by introducing VGO feed stream 2 into the flowing lean ionic liquid stream 4 and passing the combined streams through static in-line mixer 155. Static in-line mixers are well known in the art and may include a conduit with fixed internals such as baffles, fins, and channels that mix the fluid as it flows through the conduit. In other embodiments, not illustrated, lean ionic liquid stream 4 may be introduced into VGO feed stream 2, or the lean ionic liquid stream 4 and VGO feed stream may be combined such as through a “Y” conduit. In another embodiment, lean ionic liquid stream 4 and VGO feed stream 2 are separately introduced into the static in-line mixer 155. In other embodiments, the streams may be mixed by any method well know in the art including stirred tank and blending operations. The mixture comprising VGO and ionic liquid is transferred to separation zone 300 via transfer conduit 7. Separation zone 300 comprises separation vessel 165 wherein the two phases are allowed to separate into a rich ionic liquid phase which is withdrawn from a lower portion of separation vessel 165 via ionic liquid effluent conduit 8 and the VGO phase is withdrawn from an upper portion of separation vessel 165 via VGO effluent conduit 6. Separation vessel 165 may comprise a boot, not illustrated, from which rich ionic liquid is withdrawn via conduit 8.

Separation vessel 165 may contain a solid media 175 and/or other coalescing devices which facilitate the phase separation. In other embodiments the separation zone 300 may comprise multiple vessels which may be arranged in series, parallel, or a combination thereof. The separation vessels may be of any shape and configuration to facilitate the separation, collection, and removal of the two phases. In a further embodiment, sulfur removal zone 100 may include a single vessel wherein lean ionic liquid stream 4 and VGO feed stream 2 are mixed, then remain in the vessel to settle into the VGO effluent and rich ionic liquid phases. In an embodiment the process comprises at least two sulfur removal steps. For example, the VGO effluent from one sulfur removal step may be passed directly as the VGO feed to a second sulfur removal step. In another embodiment, the VGO effluent from one sulfur removal step may be treated or processed before being introduced as the VGO feed to the second sulfur removal step. There is no requirement that each sulfur removal zone comprises the same type of equipment. Different equipment and conditions may be used in different sulfur removal zones.

The sulfur removal step may be conducted under sulfur removal conditions including temperatures and pressures sufficient to keep the VGO-immiscible ionic liquid and VGO feeds and effluents as liquids. For example, the sulfur removal step temperature may range between about 10° C. and less than the decomposition temperature of the ionic liquid; and the pressure may range between about atmospheric pressure and about 700 kPa(g). When the VGO-immiscible ionic liquid comprises more than one ionic liquid component, the decomposition temperature of the ionic liquid is the lowest temperature at which any of the ionic liquid components decompose. The sulfur removal step may be conducted at a uniform temperature and pressure or the contacting and separating steps of the sulfur removal step may be operated at different temperatures and/or pressures. In an embodiment, the contacting step is conducted at a first temperature, and the separating step is conducted at a temperature at least 5° C. lower than the first temperature. In a non limiting example the first temperature is about 80° C. Such temperature differences may facilitate separation of the VGO and ionic liquid phases.

The above and other sulfur removal step conditions such as the contacting or mixing time, the separation or settling time, and the ratio of VGO feed to VGO-immiscible ionic liquid (lean ionic liquid) may vary greatly based, for example, on the specific ionic liquid or liquids employed, the nature of the VGO feed (straight run or previously processed), the sulfur content of the VGO feed, the degree of sulfur removal required, the number of sulfur removal steps employed, and the specific equipment used. In general it is expected that contacting time may range from less than one minute to about two hours; settling time may range from about one minute to about eight hours; and the weight ratio of VGO feed to lean ionic liquid introduced to the sulfur removal step may range from 1:10,000 to 10,000:1. In an embodiment, the weight ratio of VGO feed to lean ionic liquid may range from about 1:1,000 to about 1,000:1; and the weight ratio of VGO feed to lean ionic liquid may range from about 1:100 to about 100:1. In an embodiment the weight of VGO feed is greater than the weight of ionic liquid introduced to the sulfur removal step.

In an embodiment, a single sulfur removal step reduces the sulfur content of the vacuum gas oil by at least 3 wt %. In another embodiment, the sulfur content of the vacuum gas oil is reduced by at least 15 wt % in a single sulfur removal step; and the sulfur content of the vacuum gas oil may be reduced by at least 60 wt % in a single sulfur removal step. As discussed herein the invention encompasses multiple sulfur removal steps to provide the desired amount of sulfur removal. The degree of phase separation between the VGO and ionic liquid phases is another factor to consider as it affects recovery of the ionic liquid and VGO. The degree of sulfur removed and the recovery of the VGO and ionic liquids may be affected differently by the nature of the VGO feed, the specific ionic liquid or liquids, the equipment, and the sulfur removal conditions such as those discussed above.

The amount of water present in the vacuum gas oil/VGO-immiscible ionic liquid mixture during the sulfur removal step may also affect the amount of sulfur removed and/or the degree of phase separation, i.e. recovery of the VGO and ionic liquid. In an embodiment, the VGO/VGO-immiscible ionic liquid mixture has a water content of less than about 10% relative to the weight of the ionic liquid. In another embodiment, the water content of the VGO/VGO-immiscible ionic liquid mixture is less than about 5% relative to the weight of the ionic liquid; and the water content of the VGO/VGO-immiscible ionic liquid mixture may be less than about 2% relative to the weight of the ionic liquid. In a further embodiment, the VGO/VGO-immiscible ionic liquid mixture is water free, i.e. the mixture does not contain water.

FIG. 1 is a flow scheme illustrating various embodiments of the invention and some of the optional and/or alternate steps and apparatus encompassed by the invention. Vacuum gas oil stream 2 and VGO-immiscible ionic liquid stream 4 are introduced to and contacted and separated in sulfur removal zone 100 to produce VGO-immiscible ionic liquid effluent stream 8 and vacuum gas oil effluent stream 6 as described above. The ionic liquid stream 4 may be comprised of fresh ionic liquid stream 3 and/or one or more ionic liquid streams which are recycled in the process as described below. In an embodiment, a portion or all of vacuum gas oil effluent stream 6 is passed via conduit 10 to a hydrocarbon conversion zone 800. Hydrocarbon conversion zone 800 may, for example, comprise at least one of an FCC and a hydrocracking process which are well known in the art.

An optional VGO washing step may be used, for example, to recover ionic liquid that is entrained or otherwise remains in the VGO effluent stream by using water to wash or extract the ionic liquid from the VGO effluent. In this embodiment, a portion or all of VGO effluent stream 6 (as feed) and a water stream 12 (as solvent) are introduced to VGO washing zone 400. The VGO effluent and water streams introduced to VGO washing zone 400 are mixed and separated to produce a washed vacuum gas oil stream 14 and a spent water stream 16, which comprises the ionic liquid. The VGO washing step may be conducted in a similar manner and with similar equipment as used to conduct other liquid-liquid wash and extraction operations as discussed above. Various VGO washing step equipment and conditions such as temperature, pressure, times, and solvent to feed ratio may be the same as or different from the sulfur removal zone equipment and conditions. In general, the VGO washing step conditions will fall within the same ranges as given above for the sulfur removal step conditions. A portion or all of the washed vacuum gas oil stream 14 may be passed to hydrocarbon conversion zone 800.

An optional ionic liquid regeneration step may be used, for example, to regenerate the ionic liquid by removing the sulfur compound from the ionic liquid, i.e. reducing the sulfur content of the rich ionic liquid. In an embodiment, a portion or all of VGO-immiscible ionic liquid effluent stream 8 (as feed) comprising the sulfur compound and a regeneration solvent stream 18 are introduced to ionic liquid regeneration zone 500. The VGO-immiscible ionic liquid effluent and regeneration solvent streams are mixed and separated to produce an extract stream 20 comprising the sulfur compound, and a regenerated ionic liquid stream 22. The ionic liquid regeneration step may be conducted in a similar manner and with similar equipment as used to conduct other liquid-liquid wash and extraction operations as discussed above. Various ionic liquid regeneration step conditions such as temperature, pressure, times, and solvent to feed may be the same as or different from the sulfur removal conditions. In general, the ionic liquid regeneration step conditions will fall within the same ranges as given above for the sulfur removal step conditions.

In an embodiment, the regeneration solvent stream 18 comprises a hydrocarbon fraction lighter than VGO and which is immiscible with the VGO-immiscible ionic liquid. The lighter hydrocarbon fraction may consist of a single hydrocarbon compound or may comprise a mixture of hydrocarbons. In an embodiment, the lighter hydrocarbon fraction comprises at least one of a naphtha, gasoline, diesel, light cycle oil (LCO), and light coker gas oil (LCGO) hydrocarbon fraction. The lighter hydrocarbon fraction may comprise straight run fractions and/or products from conversion processes such as hydrocracking, hydrotreating, fluid catalytic cracking (FCC), reforming, coking, and visbreaking In this embodiment, extract stream 20 comprises the lighter hydrocarbon regeneration solvent and the sulfur compound. In another embodiment, the regeneration solvent stream 18 comprises water and the ionic liquid regeneration step produces extract stream 20 comprising the sulfur compound and regenerated VGO-immiscible ionic liquid 22 comprising water and the ionic liquid. In an embodiment wherein regeneration solvent stream 18 comprises water, a portion or all of spent water stream 16 may provide a portion or all of regeneration solvent stream 18. Regardless of whether regeneration solvent stream 18 comprises a lighter hydrocarbon fraction or water, a portion or all of regenerated VGO-immiscible ionic liquid stream 22 may be recycled to the sulfur removal step via a conduit not shown consistent with other operating conditions of the process. For example, a constraint on the water content of the VGO-immiscible ionic liquid stream 4 or ionic liquid/VGO mixture in sulfur removal zone 100 may be met by controlling the proportion and water content of fresh and recycled ionic liquid streams.

Optional ionic liquid drying step is illustrated by drying zone 600. The ionic liquid drying step may be employed to reduce the water content of one or more of the streams comprising ionic liquid to control the water content of the sulfur removal step as described above. In the embodiment of FIG. 1, a portion or all of regenerated VGO-immiscible ionic liquid stream 22 is introduced to drying zone 600. Although not shown, other streams comprising ionic liquid such as the fresh ionic liquid stream 3, VGO-immiscible ionic liquid effluent stream 8, and spent water stream 16, may also be dried in any combination in drying zone 600. To dry the ionic liquid stream or streams, water may be removed by one or more various well known methods including distillation, flash distillation, and using a dry inert gas to strip water. Generally, the drying temperature may range from about 100° C. to less than the decomposition temperature of the ionic liquid, usually less than about 300° C. The pressure may range from about 35 kPa(g) to about 250 kPa(g). The drying step produces a dried VGO-immiscible ionic liquid stream 24 and a drying zone water effluent stream 26. Although not illustrated, a portion or all of dried VGO-immiscible ionic liquid stream 24 may be recycled or passed to provide all or a portion of the VGO-immiscible ionic liquid introduced to sulfur removal zone 100. A portion or all of drying zone water effluent stream 26 may be recycled or passed to provide all or a portion of the water introduced into VGO washing zone 400 and/or ionic liquid regeneration zone 500.

Unless otherwise stated, the exact connection point of various inlet and effluent streams within the zones is not essential to the invention. For example, it is well known in the art that a stream to a distillation zone may be sent directly to the column, or the stream may first be sent to other equipment within the zone such as heat exchangers, to adjust temperature, and/or pumps to adjust the pressure. Likewise, streams entering and leaving sulfur removal, washing, and regeneration zones may pass through ancillary equipment such as heat exchanges within the zones. Streams, including recycle streams, introduced to washing or extraction zones may be introduced individually or combined prior to or within such zones.

The invention encompasses a variety of flow scheme embodiments including optional destinations of streams, splitting streams to send the same composition, i.e. aliquot portions, to more than one destination, and recycling various streams within the process. Examples include: various streams comprising ionic liquid and water may be dried and/or passed to other zones to provide all or a portion of the water and/or ionic liquid required by the destination zone. The various process steps may be operated continuously and/or intermittently as needed for a given embodiment e.g. based on the quantities and properties of the streams to be processed in such steps. As discussed above the invention encompasses multiple sulfur removal steps, which may be performed in parallel, sequentially, or a combination thereof. Multiple sulfur removal steps may be performed within the same sulfur removal zone and/or multiple sulfur removal zones may be employed with or without intervening washing, regeneration and/or drying zones.

EXAMPLES

The examples are presented to further illustrate some aspects and benefits of the invention and are not to be considered as limiting the scope of the invention.

Example 1

A commercial sample of a hydrotreated vacuum gas oil (HTVGO) with the following properties was obtained for use a feed stream. The HTVGO contained 1162 ppm-wt sulfur as determined by ASTM method D5453-00, Ultraviolet Fluorescence, and 451 ppm-wt nitrogen as determined by ASTM method D4629-02, Trace Nitrogen in Liquid Petroleum Hydrocarbons by Syringe/Inlet Oxidative Combustion and Chemiluminescence Detection. The boiling point range of the HTVGO shown in Table 1 was determined by ASTM method D-2887.

TABLE 1

Temp. ° C.


IBP 99
5%  278
25% 377
50% 425
75% 468
95% 523
FBP 566

Example 2

A commercial sample of a straight run, i.e., not processed after the crude distillation, vacuum gas oil (VGO) with the following properties was obtained for use a feed stream. The VGO contained 5800 ppm-wt sulfur as determined by ASTM method D5453-00 and 1330 ppm-wt nitrogen as determined by ASTM method D4629-02. The boiling point range of the VGO shown in Table 2 was determined by ASTM method D-2887.

TABLE 2

Temp. ° C.


IBP 263
5%  330
25% 394
50% 443
75% 500
95% 569
FBP 608

Example 3-12

The HTVGO of Example 1 and an ionic liquid listed in Table 3 were added to a vial containing a magnetic stir bar in a HTVGO to ionic liquid weight ratio of 2:1. The contents were mixed at 80° C. and 300 rpm for 30 minutes using a digitally controlled magnetic stirrer hot plate. After mixing was stopped, the samples were held static at 80° C. for 30 minutes then a sample of the HTVGO phase (VGO effluent) was removed with a glass pipette and analyzed by ASTM method D5453-00 for sulfur. The results are compared in Table 3 where the amounts of sulfur removed from the HTVGO are reported on a wt % sulfur basis.

TABLE 3
		Sulfur
		removed from
Example	Ionic Liquid	HTVGO, wt %
3	1-butyl-3-methylimidazolium chloride	4.0
4	1-butyl-3-methylimidazolium	64.5
	trifluoromethanesulfonate
5	1-butyl-4-methylpyridinium chloride	15.8
6	N-butyl-3-methylpyridinium methylsulfate	7.1
7	tetrabutylphosphonium methanesulfonate	4.0
8	trihexyl(tetradecyl)phosphonium chloride	15.3
9	trihexyl(tetradecyl)phosphonium bromide	28.1
10	tetradecyl(trihexyl)phosphonium bis-2,4,4	No phase
	(trimethylpentyl)phosphinate	separation
11	triisobutyl(methyl)phosphonium tosylate	5.0
12	tributyl(ethyl)phosphonium diethylphosphate	22.4

Examples 13-23

The same conditions and procedure as used in Examples 7-12 were repeated in Examples 13-18 except the VGO of Example 2 and an ionic liquid listed in Table 4 were used. The results for additional ionic liquids and the VGO of Example 2 are given in Examples 19-23. Table 4 provides a comparison of the amount of sulfur removed from the VGO on a wt % sulfur basis for Examples 13-23.

TABLE 4
		Sulfur removed
		from VGO,
Example	Ionic Liquid	wt %
13	tetrabutylphosphonium methanesulfonate	5.2
14	trihexyl(tetradecyl)phosphonium chloride	*
15	trihexyl(tetradecyl)phosphonium bromide	22.4
16	tetradecyl(trihexyl)phosphonium bis-2,4,4	No phase
	(trimethylpentyl)phosphinate	separation
17	triisobutyl(methyl)phosphonium tosylate	3.4
18	tributyl(ethyl)phosphonium diethylphosphate	10.3
19	tributyl(methyl)phosphonium methylsulfate	*
20	tributyl(methyl)phosphonium chloride	3.8
21	tributyl(hexyl)phosphonium chloride	9.2
22	tributyl(octyl)phosphonium chloride	10.5
23	tetrabutylphosphonium chloride	7.0
* After 30 minutes of settling time phase separation had started but was insufficient to obtain a meaningful sample of VGO for analysis.

Examples 3-23 illustrate that a VGO-immiscible ionic liquid comprising at least one of an imidazolium ionic liquid, a pyridinium ionic liquid, and a phosphonium ionic liquid removes sulfur from vacuum gas oil. The results also demonstrate the unpredictable nature of this art as the results vary significantly between groups of ionic liquids and even within a group of similar ionic liquids. The results also vary with different VGO feeds.

Claims

1. A process for removing a sulfur compound from a vacuum gas oil comprising:

(a) contacting the vacuum gas oil comprising the sulfur compound with a vgo-immiscible ionic liquid to produce a mixture comprising the vacuum gas oil and the vgo-immiscible ionic liquid, the vgo-immiscible ionic liquid comprising at least one of an imidazolium ionic liquid, a pyridinium ionic liquid, and a phosphonium ionic liquid; and

(b) separating the mixture to produce a vacuum gas oil effluent and a vgo-immiscible ionic liquid effluent, the vgo-immiscible ionic liquid effluent comprising the sulfur compound;

wherein the vgo-immiscible ionic liquid comprises at least one ionic liquid from at least one of 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-4-methylpyridinium chloride, N-butyl-3-methylpyridinium methylsulfate,

trihexyl(tetradecyl)phosphonium chloride, trihexyl(tetradecyl)phosphonium bromide, tributyl(methyl)phosphonium bromide, tributyl(methyl)phosphonium chloride, tributyl(hexyl)phosphonium bromide, tributyl(hexyl)phosphonium chloride, tributyl(octyl)phosphonium bromide, tributyl(octyl)phosphonium chloride, tributyl(decyl)phosphonium bromide, tributyl(decyl)phosphonium chloride, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, triisobutyl(methyl)phosphonium tosylate, tributyl(ethyl)phosphonium diethylphosphate, tetrabutylphosphonium methanesulfonate,

wherein the sulfur content of the vacuum gas oil is reduced by at least 20-80%;

further comprising contacting the vgo-immiscible ionic liquid effluent with a regeneration solvent and separating the vgo-immiscible ionic liquid effluent from the regeneration solvent to produce an extract stream comprising the sulfur compound and a regenerated vgo-immiscible ionic liquid stream wherein the regeneration solvent comprises water and the regenerated vgo-immiscible ionic liquid stream comprises water; and

wherein the vacuum gas oil effluent comprises vgo-immiscible ionic liquid, the process further comprising washing at least a portion of the vacuum gas oil effluent with water to produce a washed vacuum gas oil stream and a spent water stream, the spent water stream comprising the vgo-immiscible ionic liquid; wherein at least a portion of the spent water stream is at least a portion of the regeneration solvent.

2. The process of claim 1 further comprising drying at least a portion of at least one of the regenerated vgo-immiscible ionic liquid stream and the spent water stream to produce a dried vgo-immiscible ionic liquid stream.

3. The process of claim 2 further comprising recycling at least a portion of the dried vgo-immiscible ionic liquid stream to the sulfur removal contacting step.

4. A process for removing a sulfur compound from a vacuum gas oil comprising:

(a) contacting the vacuum gas oil comprising the sulfur compound with a vgo-immiscible ionic liquid to produce a mixture comprising the vacuum gas oil, and the vgo-immiscible ionic liquid, the vgo-immiscible ionic liquid comprising at least one of an imidazolium ionic liquid, a pyridinium ionic liquid, and a phosphonium ionic liquid;

(b) separating the mixture to produce a vacuum gas oil effluent and a vgo-immiscible ionic liquid effluent, the vgo-immiscible ionic liquid effluent comprising the sulfur compound; and

at least one of:

(c) washing at least a portion of the vacuum gas oil effluent with water to produce a washed vacuum gas oil stream and a spent water stream;

(d) contacting the vgo-immiscible ionic liquid effluent with a regeneration solvent and separating the vgo-immiscible ionic liquid effluent from the regeneration solvent to produce an extract stream comprising the sulfur compound and a regenerated vgo-immiscible ionic liquid stream; and

(e) drying at least a portion of at least one of the vgo-immiscible ionic liquid effluent, the spent water stream, and the regenerated vgo-immiscible ionic liquid stream to produce a dried vgo-immiscible ionic liquid stream.

5. The process of claim 4 further comprising recycling at least a portion of at least one of the vgo-immiscible ionic liquid effluent, the spent water stream, the regenerated vgo-immiscible ionic liquid stream, and the dried vgo-immiscible ionic liquid stream to the sulfur removal contacting step.